Patients with high-grade serous ovarian cancer (HGSOC) are commonly diagnosed after extensive metastasis has occurred, resulting in a poor prognosis. In HGSOC, metastasis occurs primarily by transcoelomic spread, where tumor cells detach from the primary tumor, float through the peritoneal fluid, and attach to the mesothelial layer lining the peritoneal cavity to form new metastases. During this process, mesothelial cells clear away from the tumor cells through collective migration, causing a gap to form in the mesothelial layer. However, it is unknown what factors regulate mesothelial cell clearance, which prohibits the development of therapies to slow or stop this stage of metastasis. As collective migration ultimately results from forces, we expect that studying the balance of forces within the cell layer will identify mechanical factors that regulate clearance. Additionally, the onset of transcoelomic spread correlates with the accumulation of ascites fluid, which includes a complex mixture of soluble factors that are known to impact the magnitude of forces. Therefore, we hypothesize that ascites fluid accelerates mesothelial clearance by altering the mechanics of the mesothelial cell monolayer to support faster collective migration away from the tumor cells. We will address this hypothesis with the following aims, which each integrate experimental approaches and computational modeling: Specific Aim 1: Identify soluble factors in ascites fluid that support mesothelial clearance. Specific Aim 2: Determine how mesothelial clearance depends on the balance of cell-cell tension and cell- substrate traction in the mesothelial layer. Completion of the proposed studies will result in an improved understanding of the mechanical process of mesothelial cell clearance and the identification of potential therapeutic targets to slow or stop metastasis in HGSOC.